The study of disease processes in the human eye by current methods of electron microscopy is hampered by the difficulties in obtaining suitable material. It is often difficult, or even impossible to prepare such material by the most suitable techniques for electron microscopic study. Extensive retrospective studies of tissues properly prepared in this way are, as yet, not feasible. It has been found that useful information in regard to many special problems, both current and retrospective, that cannot be obtained by light microscopy alone, can be obtained by electron microscopic examination of tissues heretofore considered "improperly prepared." These tissues are derived from such diverse sources as autopsy material (44), surgically enucleated eyes (21, 46), paraffin-embedded tissues (34, 38-40) (and "wet tissues" (1, 21, 28), as well as minute biopsy specimens (13, 20) too small for proper light microscopic study. The investigators propose to expand their studies of such materials which have already proved to be a good source of valuable information (e.g., in the "differential diagnosis of leiomyoma of the ciliary body (28), or "on the nature of retinoblastoma" (38, 40) as well as in a number of other disease entities).